7. sizing off grid.pdf

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    Wp

    PV system sizing

     

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    1. Site survey (structures, electrical consumers, meteorlogical data)

    2. Determine consumer energy demand3. System voltage (12,24,48, 230V ?) 4. Determine PV array power

     . eterm ne attery capac ty an vo tage 6. Determine charge controller voltage and

    current

    7. Determine inverter power 8. Determine cable size

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    System voltage, depends on:

    - Electrical devices (ac or dc) - Energy demand (approx. up to

    1KVAh – 12V, up to 2,5KVAh – 24V...)

    - Cable lengths PV – battery and battery – el. consumer

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    Consumer energy demand: - Real power rating of ac devices (apparent

    power) - Efficiency of inverter(app. 85-95%)

    - . of rated power)

    - Running time of devices (incl. Inverter)

    = Battery discharge in Wh

    divide by System Voltage

    = Battery discharge in Ah

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    Consumer Power demand: Device Wattage = inverter output power (VA)

    cos phi

    Inverter output = inverter input power (VA) Inv. eff.

    -

    Inverter

    Output (VA)Input (VA)

    Standby

     

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    Consumer Energy demand: inverter input x hours = energy demand devices

    inverter own consumption x hours = inverter energy demand

    energy demand devices + inverter energy demand

    =

    consumer energy demand (VAh) = Battery discharge (Ah) Battery Voltage

    Battery discharge (Ah) = Battery Capacity

    DoD

    Battery sizing:

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    Battery discharge

    Battery char e

    C (Ah)

    (Wh / Ah)

     

    (Wh / Ah)

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    Consumer

    energy PV energy demand

    Hours ?

    Power ?

    Cos Phi ?

    Standby?

    Eff.?

    Out of MPP

    operation losses

    25%

    P   e r f    o r 

    Charging

    losses 5%

     

    = Battery Discharge

    (Wh)

    = Battery Charge (Wh)

    Electric losses 5%

    m a n  c  e

         6      5     %

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    100Wh 65WhPV energy demand Consumer energy demand

    Losses 35%

    100Wh x 65% = 65Wh

    65Wh / 65% = 100Wh

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    Performance ratio (PR)

    95%

     

    65%

     en ca cu a ng • Current increases slightly

    with temperature and at

    operating point (app. 5%) • losses for dust • battery losses • charge controller losses

    • wiring losses

    en ca cu a ng • operating voltage (13,5V)

    is app 25% less than Vmpp

    • losses for dust • battery losses • charge controller losses • wiring losses

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    PV energy demand , Battery charge

    = Battery discharge PerformanceRatio

    PV Power , PV Current

    = PV energy demand Peak sun hours

    Choose the right module and quantity

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    Battery sizing:

    consumer energy demand (VAh) = Battery discharge (Ah) Battery Voltage

    Battery discharge (Ah) = Battery Capacity

    o

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    Battery capacity depends on:

    • daily battery discharge (Ah)  

    • Autonomy days

    battery discharge x Autonomy days DoDC =

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    Charge controller size depends on:

    • current from PV module(s)  

    Add 20%

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    Inverter size depends on:

    • peak load of ac devices  

    Add 100% for CFL due to harmonics Consider starting current of motors

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    cable size depends on:

    • desired max voltage drop • length

    • current

    Allow max 3% voltage drop from PV to battery and from battery to consumer